1. Field of the Invention
The present invention relates to a substrate having an SOI structure, which is formed by bonding a semiconductor layer formed from a thin slice of a crystalline semiconductor substrate to a different kind of substrate. In particular, the present invention relates to a bonding SOI technique, and also relates to a manufacturing method of an SOI substrate in which a single-crystalline or polycrystalline semiconductor layer is bonded to a substrate having an insulating surface such as a glass substrate. Further, the present invention relates to a display device or a semiconductor device using such a substrate having an SOI structure.
2. Description of the Related Art
A semiconductor substrate called a silicon-on-insulator (SOI substrate) that has a thin single-crystalline semiconductor layer on an insulating layer has been developed instead of a silicon wafer that is manufactured by thinly slicing an ingot of a single-crystalline semiconductor, and the SOI substrate is spreading as a substrate in manufacturing a microprocessor or the like. This is because an integrated circuit using an SOI substrate draws attention as an integrated circuit in which parasitic capacitance between drains of transistors and a substrate can be reduced, performance of the semiconductor integrated circuit can be improved, and low power consumption is achieved.
As a method for manufacturing SOI substrates, a hydrogen ion implantation separation method is known (for example, see Patent Document 1: U.S. Pat. No. 6,372,609). The hydrogen ion implantation separation method is a method in which hydrogen ions are implanted into a silicon wafer to form a microbubble layer at a predetermined depth from the surface, and a thin silicon layer (SOI layer) is bonded to another silicon wafer using the microbubble layer as a cleavage plane. In addition to the heat treatment for separation of an SOI layer, it is necessary to perform heat treatment in an oxidizing atmosphere to form an oxide film on the SOI layer, remove the oxide film, and perform heat treatment at 1000° C. to 1300° C. in a reducing atmosphere to increase bonding strength.
On the other hand, forming an SOI layer on an insulating substrate such as glass is also attempted. As an example of SOI substrates in which SOI layers are formed on glass substrates, an SOI substrate in which a thin single-crystalline silicon layer is formed over a glass substrate having a coating film by a hydrogen ion implantation separation method is known (see Patent Document 2: U.S. Pat. No. 7,119,365). In this case also, the thin silicon layer (SOI layer) is formed over the glass substrate in such a way that a microbubble layer is formed at a predetermined depth from the surface by implantation of hydrogen ions to a single-crystalline silicon wafer, the glass substrate and the single-crystalline silicon wafer are bonded, and the silicon wafer is separated using the microbubble layer as a cleavage plane.